Isometric work is a great way to pack muscle on to your upper back, improve posture, and bulletproof your shoulders... and it's also kind of boring. Liven things up with this variation.
Initiate each rep from the isometric portion of the exercise. You'll build a stronger, wider, more resilient upper back. You'll also bump up your performance in pressing and pushing exercises due to improved shoulder/scapular stability.
The occlusion effect you'll get from the isometric holds will also give you a pretty wicked pump, not to mention the extra work your grip and forearms are going to get.
These also work great on a flat bench, though you'll need to elevate the bench to allow your arms to fully extend.